Olmesartan is an angiotensin receptor blocker (ARB) and is widely used in clinical practice to treat hypertension. To compare the pharmacokinetic (PK) parameters and tolerability of two oral formulations of olmesartan (test drug: OMETAN(R) 20 mg tablet, reference drug: OLMETEC(R) 20 mg tablet) and assess their bioequivalence, a randomized, single dose, two-treatment crossover clinical study was conducted. At each period, 40 subjects received the test drug or the reference drug. Blood samples were collected at pre-dose and up to 48 h after study drug administration of each period. Plasma concentrations of olmesartan were measured using liquid chromatography-tandem mass spectrometry. To evaluate PK profiles, maximum plasma concentration (C(max)) and area under the concentration-time curve from zero to last measurable time (AUC(last)) were estimated using a non-compartmental method. Tolerability was evaluated based on the incidence of adverse events, vital signs, electrocardiograms, and laboratory tests. A total of 39 subjects completed the study. The geometric mean ratio and 90% confidence intervals (CI) of test drug to reference drug were 1.027 (0.969-1.088) for C(max) and 1.014 (0.957-1.074) for AUC(last), respectively. There were no serious adverse events and both formulations of olmesartan were well tolerated. The OMETAN 20 mg tablet was judged to be bioequivalent to the OLMETEC 20 mg tablet.